Display substrate with improved carrier mobility of thin film transistors within GOA region

ABSTRACT

The present disclosure relates to the field of display technology, and provides a display substrate, its manufacturing method, and a display device. The display substrate includes a display region and a GOA region. An active layer of a TFT at the GOA region at least includes a first oxide semiconductor layer and a second oxide semiconductor layer arranged on the first oxide semiconductor layer, and the first oxide semiconductor layer is arranged between the second oxide semiconductor layer and a base substrate of the display substrate and has a carrier mobility of smaller than the second oxide semiconductor layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is the U.S. national phase of PCT ApplicationNo. PCT/CN2020/075727 filed on Feb. 18, 2020, which claims a priority ofthe Chinese patent application 201910289224.1 filed on Apr. 11, 2019,which are incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present disclosure relates to the field of display technology, inparticular to a display substrate, its manufacturing method, and adisplay device.

BACKGROUND

The display technology is moving in a direction of a larger resolutionand a narrower bezel, and it is currently an important trend in thedevelopment of an Organic Light-Emitting Diode (OLED) display product toprovide a narrow bezel.

SUMMARY

In one aspect, the present disclosure provides in some embodiments adisplay substrate, including a display region and a gate driver on array(GOA) region. An active layer of a thin film transistor (TFT) at the GOAregion at least includes a first oxide semiconductor layer and a secondoxide semiconductor layer arranged on the first oxide semiconductorlayer, and the first oxide semiconductor layer is arranged between thesecond oxide semiconductor layer and a base substrate of the displaysubstrate and has a carrier mobility of smaller than the second oxidesemiconductor layer.

In some possible embodiments of the present disclosure, an active layerof a TFT at the display region merely includes the first oxidesemiconductor layer.

In some possible embodiments of the present disclosure, the carriermobility of the second oxide semiconductor layer is more than 30cm²/(V·S).

In some possible embodiments of the present disclosure, the second oxidesemiconductor layer is made of IGZYO or IGTO, where Y represents Sn.

In some possible embodiments of the present disclosure, a content of Inis six times of a content of Ga in the second oxide semiconductor layer,and a content of O accounts for 10% to 35%.

In some possible embodiments of the present disclosure, contents ofelements in IGZYO meet an equation of In:Ga:Zn:Sn=6:1:4:1.

In some possible embodiments of the present disclosure, the first oxidesemiconductor layer is made of IGZO.

In some possible embodiments of the present disclosure, the first oxidesemiconductor layer has a thickness of 300 to 500 Å.

In some possible embodiments of the present disclosure, the TFT is atop-gate TFT.

In some possible embodiments of the present disclosure, the second oxidesemiconductor layer has a thickness of 300 to 500 Å.

In some possible embodiments of the present disclosure, the TFT at theGOA region has a carrier mobility within a range from 20.5 cm²/(V·S) to30.2 cm²/(V·S).

In another aspect, the present disclosure provides in some embodiments adisplay device including the above-mentioned display substrate.

In some possible embodiments of the present disclosure, the displaydevice is an OLED display device.

In yet another aspect, the present disclosure provides in someembodiments a method for manufacturing a display substrate, the displaysubstrate including a display region and a GOA region, the methodincluding forming a first oxide semiconductor layer and a second oxidesemiconductor layer sequentially at the GOA region, and patterning thesecond oxide semiconductor layer and the first oxide semiconductor layerto form an active layer of a TFT. The first oxide semiconductor layerhas a carrier mobility smaller than the second oxide semiconductorlayer.

In some possible embodiments of the present disclosure, the methodfurther includes forming an active layer of a TFT at the display regionby the first oxide semiconductor layer.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to illustrate the technical solutions of the present disclosureor the related art in a clearer manner, the drawings desired for thepresent disclosure or the related art will be described hereinafterbriefly. Obviously, the following drawings merely relate to someembodiments of the present disclosure, and based on these drawings, aperson skilled in the art may obtain the other drawings without anycreative effort.

FIG. 1 is a schematic view showing a display substrate with alight-shielding layer according to some embodiments of the presentdisclosure;

FIG. 2 is a schematic view showing the display substrate with a bufferlayer according to some embodiments of the present disclosure;

FIG. 3 is a schematic view showing the display substrate with a firstoxide semiconductor layer according to some embodiments of the presentdisclosure;

FIG. 4 is a schematic view showing the display substrate with a secondoxide semiconductor layer according to some embodiments of the presentdisclosure;

FIG. 5 is a schematic view showing the display substrate with a gateinsulation layer and a gate metal layer according to some embodiments ofthe present disclosure;

FIG. 6 is a schematic view showing the display substrate with patternsof the gate insulation layer and the gate metal layer according to someembodiments of the present disclosure;

FIG. 7 is a schematic view showing the display substrate with aninterlayer insulation layer according to some embodiments of the presentdisclosure;

FIG. 8 is a schematic view showing the display substrate with asource/drain metal layer according to some embodiments of the presentdisclosure; and

FIG. 9 is a schematic view showing the display substrate with apassivation layer according to some embodiments of the presentdisclosure.

REFERENCE SIGN LIST

-   -   1 base substrate    -   2 light-shielding layer    -   3 buffer layer    -   4 first oxide semiconductor layer    -   5 second oxide semiconductor layer    -   6 gate insulation layer    -   7 gate metal layer    -   8 passivation layer    -   9 first via-hole    -   10 second via-hole    -   11 source/drain metal layer    -   12 passivation layer

DETAILED DESCRIPTION

In order to make the objects, the technical solutions and the advantagesof the present disclosure more apparent, the present disclosure will bedescribed hereinafter in a clear and complete manner in conjunction withthe drawings and embodiments.

In the related art, in order to increase a carrier mobility of a TFT ata GOA region, an active layer of the TFT at the GOA region consists oftwo IGZO layers. An oxygen content in a lower IGZO layer (i.e., the IGZOlayer between an upper IGZO layer and a substrate) is adjusted so as toincrease the carrier mobility of the TFT at the GOA region. However, onone hand, the performance stability of the TFT may be adverselyaffected, and on the other hand, the carrier mobility is increasedlimitedly, i.e., the carrier mobility of the TFT is merely increasedfrom about 10 cm²/(V·S) up to 11-12 cm²/(V·S).

An object of the present disclosure is to provide a display substrate,its manufacturing method and a display device, so as to provide adisplay product with a narrow bezel.

The present disclosure provides in some embodiments a display substrate,which includes a display region and a GOA region. An active layer of aTFT at the GOA region at least includes a first oxide semiconductorlayer and a second oxide semiconductor layer arranged on the first oxidesemiconductor layer, and the first oxide semiconductor layer is arrangedbetween the second oxide semiconductor layer and a base substrate of thedisplay substrate and has a carrier mobility of smaller than the secondoxide semiconductor layer.

According to the embodiments of the present disclosure, the active layerof the TFT at the GOA region may include the first oxide semiconductorlayer and the second oxide semiconductor layer arranged on the firstoxide semiconductor layer, and the first oxide semiconductor layer mayhave the carrier mobility smaller than the second oxide semiconductorlayer. In this regard, the second oxide semiconductor layer may be madeof an oxide semiconductor material having a high carrier mobility, e.g.,IGZYO or IGTO. When the carrier mobility of the TFT at the GOA regionhas been increased, it is able to reduce a width of the TFT at the GOAregion, thereby to provide the display substrate with a narrow bezel.

In the embodiments of the present disclosure, the TFT may be a top-gateTFT or a bottom-gate TFT.

In the embodiments of the present disclosure, the display substrate mayinclude the display region and the GOA region, the display region may beused for display, and the GOA region may surround the display region.

The active layer of the TFT at the GOA region may include two or moreoxide semiconductor layers. In some possible embodiments of the presentdisclosure, the active layer of the TFT at the GOA region may consist oftwo oxide semiconductor layers laminated one on the other, so as tosimplify the structure of the active layer of the TFT and simplify themanufacture process of the TFT, thereby to reduce the manufacture of thedisplay substrate.

Further, an active layer of a TFT at the display region may be the firstoxide semiconductor layer. It is unnecessary to reduce a width of theTFT at the display region, so the first oxide semiconductor layer withexcellent stability, e.g., an IGZO layer, may be still used as theactive layer of the TFT at the display region.

In some possible embodiments of the present disclosure, the carriermobility of the second oxide semiconductor layer may be greater than 30cm²/(V·S), so as to provide the TFT at the GOA region with a highcarrier mobility.

To be specific, the second oxide semiconductor layer may be made ofIGZYO or IGTO, where Y represents Sn. The second oxide semiconductorlayer has such a characteristic as a high content of In. Usually, thecontent of In is six times of a content of Ga, so as to ensure that thecarrier mobility of the second oxide semiconductor layer is greater than30 cm²/(V·S). In addition, in order to ensure the carrier mobility, acontent of O in the second oxide semiconductor layer may be 10% to 35%,e.g., 10%, 15%, 20% or 25%. However, the content of O shall be less than30% as possible. This is because, the larger the content of O is, thelower the carrier mobility of the second oxide semiconductor layer is.

To be specific, the first oxide semiconductor layer may be made of IGZOwhich has excellent stability. The first oxide semiconductor layer mayhave a thickness of 300 to 500 Å, so as to, on one hand, increase thecarrier mobility of the TFT at the GOA region, and on the other hand,ensure the performance stability of the TFT at the GOA region.

For example, the active layer of the TFT at the GOA region may consistof an IGTO layer and an IGZO layer laminated one on another. Throughdesigning thicknesses of the IGTO layer and the IGZO layer, for the TFTat the GOA region, a threshold voltage Vth may be up to 1.28V, asubthreshold swing SS may be up to 0.29, I_(on)=5.6 mA, I_(off)=2.8*E⁻¹²and I_(on)/I_(off)=2*E⁹. Through an equation for calculating a saturatedcarrier mobility, the carrier mobility of the TFT at the GOA region maybe up to 30.2 cm²/(V·S). As compared with the active layer consisting oftwo IGZO layers, a leakage current of the TFT and a value ofI_(on)/I_(off) may be reduced obviously, so as to provide the TFT withbetter stability.

For another example, the active layer of the TFT at the GOA region mayconsist of an IGZYO layer and an IGZO layer laminated one on another.Through designing thicknesses of the IGZYO layer and the IGZO layer, forthe TFT at the GOA region, a threshold voltage Vth may be up to 1.1V, anSS may be up to 0.31, I_(on)=1.1 mA, I_(off)=6.3*E⁻¹² andI_(on)/I_(off)=7.1*E⁸. Through the equation for calculating a saturatedcarrier mobility, the carrier mobility of the TFT at the GOA region maybe up to 20.5 cm²/(V·S). As compared with the active layer consisting oftwo IGZO layers, the leakage current of the TFT and the value ofI_(on)/I_(off) may be reduced obviously, so as to provide the TFT withbetter stability. When the TFT operates at a temperature of 70° C. forone hour, a Positive Bias Threshold Shift (PBTS) may be 4.0V (0.4V to4.4V), or when the TFT is irradiated at 5000 nit for two hours, aNegative Bias Threshold and Illumination Shift (NBTIS) at 70° C. may be−2.6V (−0.4V to −3.0V).

The present disclosure further provides in some embodiments a displaydevice including the above-mentioned display substrate. The displaydevice may be any product or member having a display function, e.g.,liquid crystal display (LCD) panel, OLED display panel, television,display, digital photo frame, mobile phone or flat-panel computer. Thedisplay device may further include a flexible circuit board, a printedcircuit board and a back plate.

The present disclosure further provides in some embodiments a method formanufacturing a display substrate. The display substrate includes adisplay region and a GOA region. The method includes forming a firstoxide semiconductor layer and a second oxide semiconductor layersequentially at the GOA region, and patterning the second oxidesemiconductor layer and the first oxide semiconductor layer to form anactive layer of a TFT. The first oxide semiconductor layer has a carriermobility smaller than the second oxide semiconductor layer.

According to the embodiments of the present disclosure, the active layerof the TFT at the GOA region may include the first oxide semiconductorlayer and the second oxide semiconductor layer arranged on the firstoxide semiconductor layer, and the first oxide semiconductor layer mayhave the carrier mobility smaller than the second oxide semiconductorlayer. In this regard, the second oxide semiconductor layer may be madeof an oxide semiconductor material having a high carrier mobility, e.g.,IGZYO or IGTO. When the carrier mobility of the TFT at the GOA regionhas been increased, it is able to reduce a width of the TFT at the GOAregion, thereby to provide the display substrate with a narrow bezel.

In the embodiments of the present disclosure, the display substrate mayinclude the display region and the GOA region, the display region may beused for display, and the GOA region may surround the display region.

The active layer of the TFT at the GOA region may include two or moreoxide semiconductor layers. In some possible embodiments of the presentdisclosure, the active layer of the TFT at the GOA region may consist oftwo oxide semiconductor layers laminated one on the other, so as tosimplify the structure of the active layer of the TFT and simplify themanufacture process of the TFT, thereby to reduce the manufacture of thedisplay substrate.

The method may further include forming an active layer of a TFT at thedisplay region by the first oxide semiconductor layer. It is unnecessaryto reduce a width of the TFT at the display region, so the first oxidesemiconductor layer with excellent stability, e.g., an IGZO layer, maybe still used as the active layer of the TFT at the display region.

The method will be described hereinafter in conjunction with thedrawings and embodiments when the TFT is a top-gate TFT. The method mayinclude the following steps.

Step 1: as shown in FIG. 1, providing a base substrate 1 and forming alight-shielding layer 2 on the base substrate 1.

The base substrate 1 may be a flexible or rigid substrate. The flexiblesubstrate may be may be a polyimide (PI) substrate, and the rigidsubstrate may be a glass or quartz substrate.

To be specific, a metallic thin film may be formed on the base substrate1 through sputtering or thermal evaporation, and then patterned to forma pattern of the light-shielding layer 2. The metallic thin film may bemade of Cu, Al, Ag, Mo, Cr, Nd, Ni, Mn, Ti, Ta or W, or an alloythereof. The metallic thin film may be of a single-layered structure, ora multi-layered structure such as Cu/Mo, Ti/Cu/Ti or Mo/Al/Mo. Thelight-shielding layer 2 may shield the active layer of the TFT, so as toprevent the performance of the TFT from being adversely affected whenthe active layer is irradiated by an external light beam.

Step 2: as shown in FIG. 2, forming a buffer layer 3.

Through the buffer layer 3, it is able to prevent ions in the glass orquartz substrate from entering the TFT, thereby to prevent theperformance of the TFT from being adversely affected. To be specific,the buffer layer may be made of an oxide, a nitride or an oxynitride,e.g., SiNx, SiO₂, or both. A thickness of the buffer layer 3 may be 2000to 4000 Å.

Step 3: as shown in FIG. 3, forming the first oxide semiconductor layer4 on the buffer layer 3 at the GOA region and the display region.

The first oxide semiconductor layer 4 may be made of IGZO and have athickness of 300 to 500 Å. IGZO may be deposited at existing depositionpower and pressure, but an oxygen content of IGZO needs to be controlledwithin a range of 10% to 30%. The oxygen content needs to be smallerthan 30% as possible, so as to prevent the carrier mobility of the TFTfrom being increased too little.

To be specific, a first oxide semiconductor material may be depositedonto the buffer layer 3, and then patterned to form a pattern of thefirst oxide semiconductor layer 4.

Step 4: as shown in FIG. 4, forming the second oxide semiconductor layer5 at the GOA region.

To be specific, a second oxide semiconductor material may be deposited,and then patterned to form a pattern of the second oxide semiconductorlayer 5.

The second oxide semiconductor layer 5 may be made of an oxidesemiconductor material having a high carrier mobility, e.g., IGZYO orIGTO, where Y represents Sn, and In:Ga:Zn:Sn=6:1:4:1. Generallyspeaking, a content of In is about six times of a content of Ga, so asto ensure that the carrier mobility of the active layer is greater than30 cm²/(V·S). In addition, as shown in FIG. 4, a thickness of the secondoxide semiconductor layer 5 may be identical or similar to the thicknessof the first oxide semiconductor layer 4, e.g., within the range of 300to 500 Å. Furthermore, in order to ensure the carrier mobility of theactive layer, an oxygen content needs to be within the range of 10% to35%. For example, the oxygen content of IGZYO or IGZO may be 10%, 15%,20% or 25%. The oxygen content needs to be smaller than 30% as possible,so as to prevent the carrier mobility of the TFT from being decreased.

At the GOA region, the second oxide semiconductor layer 5 and the firstoxide semiconductor layer 4 may be laminated one on another (in adirection Y shown in FIG. 4) to form the active layer of the TFT at theGOA region. At the display region, the first oxide semiconductor layer 4may serve as the active layer of the TFT at the display region. As shownin FIG. 4, the display region is located at a right side of the GOAregion in a direction X.

Step 5: as shown in FIG. 5, forming a gate insulation layer 6 and a gatemetal layer 7.

To be specific, the gate insulation layer 6 may be deposited at atemperature of 210 to 290° C. The gate insulation layer 6 may be made ofSiO₂, and an oxygen content in an SiO₂ layer shall be increased aspossible so as to ensure the characteristic of the oxide element with ahigh carrier mobility, because oxygen may be bonded to hydrogen in theactive layer. A thickness of the gate insulation layer 6 may be withinthe range of 1000 to 2000 Å.

The gate metal layer 7 may be made of Cu, Al, Ag, Mo, Cr, Nb, Ni, Mn,Ti, Ta or W, or an alloy thereof. The gate metal layer 7 may be of asingle-layered structure, or a multi-layered structure such as Cu/Mo,Ti/Cu/Ti or Mo/Al/Mo. A thickness of the gate metal layer 7 may bewithin the range of 3000 to 5000 Å.

Step 6: as shown in FIG. 6, patterning the gate insulation layer 6 andthe gate metal layer 7, so as to form patterns of the gate insulationlayer 6 and the gate metal layer 7.

To be specific, a photoresist may be applied onto the gate metal layer7, and then exposed and developed so as to form a photoresist reservedregion and a photoresist unreserved region. Next, the gate metal layer 7at the photoresist unreserved region may be etched through a wet etchingprocess, and the gate insulation layer 6 at the photoresist unreservedregion may be etched through a dry etching process. Then, the remainingphotoresist may be removed to form the patterns of the gate insulationlayer 6 and the gate metal layer 7. An orthogonal projection of the gateinsulation layer 6 onto the base substrate may coincide with anorthogonal projection of the gate metal layer 7 onto the base substrate.The pattern of the gate metal layer 7 may include a gate electrode and agate line.

Step 7: as shown in FIG. 7, forming an interlayer insulation layer 8.

The interlayer insulation layer 8 may be made of an oxide, a nitride oran oxynitride, and specifically it may consist of a SiO₂ layer, a SiONand a SiNx layer. A thickness of the interlayer insulation layer 8 maybe within the range of 3000 to 5000 Å. The interlayer insulation layer 8may be patterned, so as to form a first via-hole 9 for exposing theactive layer and a second via-hole 10 for exposing the light-shieldinglayer.

Step 8: as shown in FIG. 8, forming a source/drain metal layer 11.

The source/drain metal layer 11 may be made of Cu, Al, Ag, Mo, Cr, Nd,Ni, Mn, Ti, Ta or W, or an alloy thereof. The source/drain metal layer11 may be of a single-layered structure, or a multi-layered structuresuch as Cu/Mo, Ti/Cu/Ti or Mo/Al/Mo. A thickness of the source/drainmetal layer 11 may be within the range of 3000 to 5000 Å. Then, thesource/drain metal layer 11 may be patterned to form a pattern of thesource/drain metal layer 11. The pattern of the source/drain metal layer11 may include a source electrode, a drain electrode and a data line.

The pattern of the source/drain metal layer 11 may be connected to theactive layer through the first via-hole 9 and connected to thelight-shielding layer 3 through the second via-hole 10. Thelight-shielding layer 3 may be connected in parallel to the pattern ofthe source/drain metal layer 11, so as to reduce a resistance of thepattern of the source/drain metal layer 11.

Step 9: as shown in FIG. 9, forming a passivation layer 12.

The passivation layer 12 may be made of an oxide, a nitride or anoxynitride, e.g., SiO₂ or SiON, and a thickness of the passivation layer12 may be within the range of 3000 to 4000 Å.

Through Steps 1 to 9, it is able to acquire a back plate of the top-gatedisplay substrate. As shown by a region B on the left in FIG. 9, at theGOA region, the second oxide semiconductor layer 5 and the first oxidesemiconductor layer 4 may be laminated one on another to form the activelayer of the TFT at the GOA region. In addition, as shown by a region Aon the right in FIG. 9, at the display region, the first oxidesemiconductor layer 4 may serve as the active layer of the TFT at thedisplay region. The second oxide semiconductor layer may be made of anoxide semiconductor material having a high carrier mobility, e.g., IGZYOor IGTO, and the first oxide semiconductor layer may be made of an oxidesemiconductor material having excellent stability, e.g., IGZO. As aresult, it is able to, on one hand, increase the carrier mobility of theTFT at the GOA region, and on the other hand, ensure the performancestability of the TFT at the GOA region. In addition, when the carriermobility of the TFT at the GOA region has been increased, it is able toreduce a width of the TFT at the GOA region, thereby to provide thedisplay substrate with a narrow bezel.

In the embodiments of the present disclosure, the order of the steps isnot limited to the serial numbers thereof. For a person skilled in theart, any change in the order of the steps shall also fall within thescope of the present disclosure if without any creative effort.

Unless otherwise defined, any technical or scientific term used hereinshall have the common meaning understood by a person of ordinary skills.Such words as “first” and “second” used in the specification and claimsare merely used to differentiate different components rather than torepresent any order, number or importance. Similarly, such words as“one” or “one of” are merely used to represent the existence of at leastone member, rather than to limit the number thereof. Such words as“include” or “including” intends to indicate that an element or objectbefore the word contains an element or object or equivalents thereoflisted after the word, without excluding any other element or object.Such words as “connect/connected to” or “couple/coupled to” may includeelectrical connection, direct or indirect, rather than to be limited tophysical or mechanical connection. Such words as “on”, “under”, “left”and “right” are merely used to represent relative position relationship,and when an absolute position of the object is changed, the relativeposition relationship will be changed too.

It should be appreciated that, in the case that such an element aslayer, film, region or substrate is arranged “on” or “under” anotherelement, it may be directly arranged “on” or “under” the other element,or an intermediate element may be arranged therebetween.

The above embodiments are for illustrative purposes only, but thepresent disclosure is not limited thereto. Obviously, a person skilledin the art may make further modifications and improvements withoutdeparting from the spirit of the present disclosure, and thesemodifications and improvements shall also fall within the scope of thepresent disclosure.

What is claimed is:
 1. A display substrate, comprising a display regionand a gate driver on array (GOA) region, wherein an active layer of athin film transistor (TFT) at the GOA region at least comprises a firstoxide semiconductor layer and a second oxide semiconductor layerarranged on the first oxide semiconductor layer, and the first oxidesemiconductor layer is arranged between the second oxide semiconductorlayer and a base substrate of the display substrate and has a carriermobility of smaller than the second oxide semiconductor layer, whereinan active layer of a TFT at the display region merely comprises thefirst oxide semiconductor layer.
 2. The display substrate according toclaim 1, wherein the carrier mobility of the second oxide semiconductorlayer is more than 30 cm²/(V·S).
 3. The display substrate according toclaim 1, wherein the second oxide semiconductor layer is made of IGZYOor IGTO, where Y represents Sn.
 4. The display substrate according toclaim 3, wherein a content of In is six times of a content of Ga in thesecond oxide semiconductor layer, and a content of O accounts for 10% to35%.
 5. The display substrate according to claim 4, wherein contents ofelements in IGZYO meet an equation of In:Ga:Zn:Sn=6:1:4:1.
 6. Thedisplay substrate according to claim 1, wherein the first oxidesemiconductor layer is made of IGZO.
 7. The display substrate accordingto claim 1, wherein the first oxide semiconductor layer has a thicknessof 300 to 500 Å.
 8. The display substrate according to claim 1, whereinthe TFT is a top-gate TFT.
 9. The display substrate according to claim1, wherein the second oxide semiconductor layer has a thickness of 300to 500 Å.
 10. The display substrate according to claim 1, wherein theTFT at the GOA region has a carrier mobility within a range from 20.5cm²/(V·S) to 30.2 cm²/(V·S).
 11. A display device, comprising a displaysubstrate, the display substrate comprising a display region and a gatedriver on array (GOA) region, wherein an active layer of a thin filmtransistor (TFT) at the GOA region at least comprises a first oxidesemiconductor layer and a second oxide semiconductor layer arranged onthe first oxide semiconductor layer, and the first oxide semiconductorlayer is arranged between the second oxide semiconductor layer and abase substrate of the display substrate and has a carrier mobility ofsmaller than the second oxide semiconductor layer, wherein an activelayer of a TFT at the display region merely comprises the first oxidesemiconductor layer.
 12. The display device according to claim 11,wherein the display device is an Organic Light-Emitting Diode (OLED)display device.
 13. A method for manufacturing a display substrate, thedisplay substrate comprising a display region and a GOA region, themethod comprising: forming a first oxide semiconductor layer and asecond oxide semiconductor layer sequentially at the GOA region;patterning the second oxide semiconductor layer and the first oxidesemiconductor layer to form an active layer of a TFT; and forming anactive layer of a TFT at the display region by the first oxidesemiconductor layer, wherein the first oxide semiconductor layer has acarrier mobility smaller than the second oxide semiconductor layer. 14.The display device according to claim 11, wherein the carrier mobilityof the second oxide semiconductor layer is more than 30 cm²/(V·S). 15.The display device according to claim 11, wherein the second oxidesemiconductor layer is made of IGZYO or IGTO, where Y represents Sn. 16.The display device according to claim 15, wherein a content of In is sixtimes of a content of Ga in the second oxide semiconductor layer, and acontent of O accounts for 10% to 35%.
 17. The display device accordingto claim 16, wherein contents of elements in IGZYO meet an equation ofIn:Ga:Zn:Sn=6:1:4:1.